1. Technical Field
The disclosed embodiments generally relate to systems for vapor collection and abatement.
2. Description of the Related Art
Contaminants can exist in subsurface soil and groundwater in the liquid or vapor phase as discrete substances and mixed with and/or dissolved in groundwater and soil gases. Various contaminants can be found in groundwater and soil, such as volatile compounds, including volatile organic compounds, nonvolatile materials, metal contaminants, and the likes Such contaminats are generally found and dealt with in the vadose (unsaturated) zone found between the surface of the earth and the water table, at the interface between the vadose zone and the water table, and in the saturated zone below the water table.
Such contaminants are a problem for many people and facilities. At many industrial and commercial facilities and waste handling and disposal sites, soil and groundwater are contaminated with suspended or water-soluble chemicals, or both. Many commercial facilities such as manufacturing companies that store chemicals must meet environmental remediation requirements by showing that off gassing from soil or groundwater contamination has been substantially eliminated or mitigated. In climates which do not experience winter temperatures low enough to cause substantial freezing of the ground, houses and light commercial buildings are often constructed on relatively shallow foundations with the ground floor, typically a concrete slab, supported directly on grade. A finish floor, e.g., asphalt tile, wood, or the like, can be installed over the concrete slab by simply setting it in a mastic adhesive trowelled onto the substrate. In geographical areas where the water table is relatively close to the surface, this construction presents certain problems when flooring is laid directly on the concrete support, because water vapor migrating from the moist soil through the concrete slab can cause the wood flooring to swell and warp, and gas vapors such as radon may infiltrate from the soil into buildings. Thus, home owners/builders/contractors often must perform remedial or radon abatement applications in order to eliminate potential health risks posed by such harmful gasses.
A variety of techniques have been used for removal of contaminants and remediation of affected soil. One common technique entails the excavation and off-site treatment of the soil. Another technique entails saturating the contaminated soil with water in situ, causing the contaminants to be leached slowly from the soil by the water. The contaminated water can then be removed. U.S. Pat. No. 5,127,764, the disclosure of which is incorporated herein by reference in its entirety, discloses a floor structure incorporating a vapor and gas barrier that is comprised of layered materials that resist penetration of vapor and gas.
Techniques have also been proposed for removing volatile organic contaminants from soil by vacuum extraction. For example, in U.S. Pat. No. 4,323,122, the disclosure of which is incorporated herein by reference in its entirety, it was proposed that a vacuum be applied in a borehole at the level of the water table, the assumption being that a contaminant such as gasoline, which is lighter than water, would float on the water table and present a layer that could be drawn off by vacuum applied to the liquid at or around that level. U.S. Pat. No. 4,323,122 also discloses a system and method for recovering organic liquid such as gasoline which has settled on the water table in underground areas. The system comprises a conduit extending from the ground surface to a point just above the water table, a collection head fitted on the lower end of the conduit, a collection vessel connected to the upper end of the conduit, and an exhaust means for creating less than atmospheric pressure in the vessel. The collection head has a liquid impermeable end portion and a liquid permeable intermediate portion for permitting the passage of liquid. The process comprises providing an opening in the ground to a point beneath the surface of the water table, positioning the conduit with the collection head in place so that the liquid permeable wall of the collection head is just above the surface of the water table, connecting the conduit to the collection vessel intake, and exhausting air and other gaseous materials from the vessel to cause liquid to flow into the collection head through the conduit into the vessel.
Other techniques include the venting of soil above the water table (i.e. in the vadose zone) to cause vaporization of the contaminant in the soil, and then drawing off the contaminant in the vapor phase. Groundwater requiring treatment is in such processes conventionally removed by pumping from separate conventional water wells. In situations in which water does flow into vacuum extraction wells, it has been suggested that a second, liquid phase pump be placed either in the well or at the surface to remove the water through a second conduit. For example, U.S. Pat. No. 4,660,639, the disclosure of which is incorporated herein by reference in its entirety, discloses a process for the removal of volatile contaminants from the vadose zone of contaminated ground by extracting volatilized contaminants from the vadose zone by way of one or more vacuum extraction wells. The process entails drilling one or more wells into the subsurface media in the contaminated area, the well being constructed so that fluids in the vadose zone can flow into the well, whereas the liquid in the saturated zone below the water table cannot substantially flow into the well, The borehole and conduit of the well can optionally extend below the water table, in which case the vacuum applied to the upper portion of the conduit will be effective to draw contaminant from the vadose zone, but insufficient to draw a significant amount of water from the saturated zone into the conduit. If it is desired to remove groundwater from below the water table, this removal is accomplished either by a separate sampling device situated in the borehole or through a separate well.
In addition, Stinson, “EPA Site Demonstration of the Terra Vac In Situ Vacuum Extraction Process in Groveland, Mass.”, Air & Waste Management Association, Vol. 39, No. 8, pages 1054 to 1062 (1989), discloses an evaluation of an in situ vacuum extraction process. The process entails removal of contaminants from the vadose zone by vacuum. Wells are installed in the contaminated vadose soil. A vacuum pump or blower induces air flow through the soil, stripping and volatilizing volatile organic compounds from the soil matrix into the air stream. Liquid water, if present in the soil, is also extracted along with the contamination. The two-phase stream of contaminated air and water flows to a vapor/liquid separator where contaminated water is removed. The contaminated air stream then flows through a treatment system such as gas-phase activated carbon to remove contaminants from the air stream. The clean air is exhausted to the atmosphere through a vent. U.S. Pat. No. 4,593,760 and U.S. Pat. No. Re. 33,102, the disclosures of which are incorporated herein by reference in their entirety, also disclose processes for removal of volatile contaminants from the vadose zone of contaminated ground by pumping volatilized contaminants from the vadose zone using one or more vacuum extraction wells.
Although known apparatus and processes are suitable for their intended purposes, they are complicated, expensive, and intrusive, requiring excavation or drilling through concrete to accomplish subsurface vacuum readings. Drilling and installation of piping through floors can be costly, and since this is still a relatively imperfect science, there is a risk of contamination if a hole is drilled where the water table is high. Moreover, traditional solutions may not provide the desired coverage de to heterogeneous subsurface conditions. The disclosure contained herein describes attempts to address one or more of the problems described above.